Known in the art is a rolling-mill roll (FR,A, 2, 169,975), comprising a mandrel with a hard-alloy sleeve provided with an element for protecting against electrochemical wear, incorporating a direct current souurce, provision being also made for a coolant fluid feeding device. The element for protection against electrochemical wear appears as anode rings rigidly fixed in circular recesses made on the periphery of the hard-alloy sleeve. The anode rings are made of a material the electric potential of which is below that of the hard alloy the sleeve is made from.
Such a construction of the roll provides for cathodic protection of the hard-alloy sleeve against electrochemical wear as follows. The anode rings in the medium of the coolant fluid which acts as electrolyte, establish a direct current source that generate current of cathodic protection of the hard-alloy sleeve against electrochemical wear.
However, the anode rings are liable to dissolution during the rolling process, with the result that their surface gets covered with the dissolution products, which disturbs electric contact between the anode rings and electrolyte. Since a potential difference at the contact interface between the anode rings and electrolyte is not high enough to overcome the resistance offered by the products of dissolution of the anode rings, the cathodic protection current is drastically diminished and might disappear altogether, which will result in electrochemical wear inflicted upon the hard-alloy sleeve working surface.
According to another embodiment of said roll the element for protection against electrochemical wear is essentially an anode shaped as a slider adapted to be pressed against the sleeve by an elastic force.
However, in such a construction the anodes are as a rule made of such non-wear-resistant materials as aluminum and magnesium, whereas the rolling speeds in modern rolling mills are as high as 100 m/s. Thus, intense wear on the spring-loaded anodes occurs, which is fraught with frequent stops for replacement of the wornout anodes.
Known in the art is another rolling-mill rolls (SU, A, 1,366,251) comprising a mandrel with a sleeve which has a slot accommodating a hard-alloy insert which has a working surface, and an element for protection against electrochemical wear, said element incorporating a direct current source, a coolant fluid feeding device being also provided. The element for protection of the hard-alloy insert working surface against electrochemical wear is essentially an anode shaped as a number of sliders fitted in the sleeve slot and adapted to contact the working surface of the hard-alloy insert. The sliders are mounted on a horizontal shaft with a possibility of a limited turning, each of them having two projections adapted to contact the respective paired work roll, with the result that the sliders move lengthwise the hard-alloy insert, whereby the oxide film is removed from the slider surface, said film resulting from anode dissolution on its surface contacting the hard-alloy insert. It is the absence of such oxide film on the anode surface that accounts for for a constant intensity of the protection (cathodic) current, the intensity of said current depending on the material of the anode and on the resistance of electrolyte (i.e., the coolant fluid). The length of the slider displacement with respect to the hard-alloy insert is very short, being as small as one millimeter per revolution of the roll so that the slider does not practically sustain any wear within a prolonged period of time.
However, since coolant fluid is fed to the roll at a high pressure, it is splashed about so that its continuity is affected, with the result that the electrical resistance of the fluid rises abruptly. The source of direct current being the anode, the cathodic current is reduced due to a high electrical resistance offered by the coolant fluid, whereas the magnitude of the cathodic protection current is not high enough to ensure against electrochemical wear on the working surface of the hard-alloy insert.